What quiet packaging revolution? The drive for low-cost packages is pushing thermoplastics into the mainstream.Electronic packaging is a hot technology topic that is evolving and unfolding ever faster as we follow our roadmap to three-dimensional (3-D) stacked designs and wafer-level package (WLP) processes. Quiet might not seem appropriate to describe the fanfare accompanying the latest multichip package (MCP (1) See Microsoft certification. (2) (MultiChip Package) A chip package that contains two or more chips. It is essentially a multichip module (MCM) that uses a laminated, printed-circuit-board-like substrate (MCM-L) rather than ceramic (MCM-C). ) and WLP technologies. But what about the new materials for these breakthrough packages? [TEXT NOT REPRODUCIBLE IN ASCII ASCII or American Standard Code for Information Interchange, a set of codes used to represent letters, numbers, a few symbols, and control characters. Originally designed for teletype operations, it has found wide application in computers. ] Building on the Basics While many new materials exist, epoxies--used for nearly 50 years as encapsulants and later in chip carriers--are still found in most new packages. And polyimide (PI) film is still the preferred material for flex-based packaging, including 3-D fold-over designs. Thermoset A polymer-based liquid or powder that becomes solid when heated, placed under pressure, treated with a chemical or via radiation. The curing process creates a chemical bond that, unlike a thermoplastic, prevents the material from being remelted. See thermoplastic. polymers, typified by epoxy molding compound (EMC (1) (EMC Corporation, Hopkinton, MA, www.emc.com) The leading supplier of storage products for midrange computers and mainframes. Founded in 1979 by Richard J. Egan and Roger Marino, EMC has developed advanced storage and retrieval technologies for the world's largest companies. ), were the obvious choice way back when plastic packaging was being developed. Once processed, it did not melt and was strong, but it was non-hermetic. Nevertheless, chip passivation passivation the final stage in instrument manufacture, passing the finished instruments through a bath of nitric acid which removes foreign particles and promotes the formation of a protective coating of chromium oxide. permitted most devices to work well enough for plastic encapsulated microelectronics (PEM) to succeed. The Emergence of Thermoplastics Today's thermoplastics, the other major class of polymers, are now superior to EMCs in critical categories. They can take the abuse of lead-free soldering, have better moisture resistance, are rapidly shaped into precise 3-D structures and are halogen free. The thermoplastic shaping processes have also kept pace. Injection molding (IM) can produce tens of thousands of packages in an hour. IM also readily produces complex 3-D cavity-style package structures. It can form a strip or array of cavity ball grid array “BGA” redirects here. For other uses, see BGA (disambiguation). A ball grid array (BGA) is a type of surface-mount packaging used for integrated circuits. (BGA) packages at high volume and low cost using economical engineering plastics like liquid crystal polymer Liquid crystal polymers (LCPs) are a unique class of wholly aromatic polyester polymers that provide previously unavailable high performance properties. In particular, they are highly inert chemically and highly resistant to fire. (LCP), the popular new flexible circuitry substrate. [ILLUSTRATION OMITTED] The ABCs of Injection Molding The IM process first liquefies plastic resin, injects it into a metal mold that may have 100 or more package-shaped cavities and then ejects finished parts. The cycle is repeated. A complete IM cycle for BGAs takes less than 10 seconds. The hot molten plastic is quickly cooled by the mold to form a tough, solid part that will not melt during soldering. IM, one of the most pervasive manufacturing processes, is used around the world to produce large and small parts for every industry, including automotive and electronics. The perfect storm of change has moved across the packaging landscape to thrust thermoplastics into the mainstream. Thermoplastics are cheap, environmentally friendly and boast near-hermetic properties far superior to non-hermetic epoxies. But the critical need for lower cost cavity packages is the catalyst. Microelectromechanical systems (MEMS (MicroElectroMechanical Systems) Tiny mechanical devices that are built onto semiconductor chips and are measured in micrometers. In the research labs since the 1980s, MEMS devices began to materialize as commercial products in the mid-1990s. ), microoptoelectromechanical systems (MOEMS See MEMS. ), radio frequency (RF) and optoelectronics (OE) have created an ever-increasing demand for low-cost, free-space enclosures best satisfied by modern thermoplastics. This quiet packaging revolution is being carried out by start-ups and other small companies, which is why it has been whispering along. A Sample Package One simple design, called low ball, insert-molds non-fusible metal balls into the plastic BGA package while it is being formed. The metal balls, captured in the plastic, protrude pro·trude v. 1. To push or thrust outward. 2. To jut out; project. through the package floor for chip connection. The bottom of each ball extends through the plastic to the outside of the package base to enable assembly to a printed wiring board (PWB). Each tiny ball thus serves as both the first- and second-level interconnect. Nothing can be simpler. Low ball could be the world's lowest cost cavity BGA. The complete package can be produced automatically in a single machine--a modified injection molding press. Low ball is just one of many thermoplastic packages under development. Another design, Flip2Stack, is intended for multiple die configured in planar and stacked configurations. The packages can be made stackable with interconnects on the bottom and top. Thermoplastics and the injection molding process offer simplification, precision and sophistication so·phis·ti·cate v. so·phis·ti·cat·ed, so·phis·ti·cat·ing, so·phis·ti·cates v.tr. 1. To cause to become less natural, especially to make less naive and more worldly. 2. . So keep listening for the quiet revolution and the inevitable drum roll. Dr. Ken Gilleo Dr. Ken Gilleo is with ET-Trends LLC; email: et-trends@cox.net. |
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